The present invention relates to a device and method for use in the petroleum industry for downhole sand clean-out operations.
Certain oil producing formations contain unconsolidated sand and other debris which can be produced with the oil. The sand and debris can collect on the wellbore, reducing the flow area and restricting production rates. In order to restore the well to maximum capacity, the sand must be removed.
Existing sand clean-out methods include the following:
(1) STROKE PUMPS--Stroke pump clean-out tools utilize a large bore reciprocating (stroke) type pump to lift sand laden fluid to surface. These pumps are typically too large to enter the smaller diameter liners encountered at the horizontal section of most wells and must be kept in the larger diameter upper casing string. Since the wells to be cleaned typically do not support a column of fluid to surface and the pump must be submerged, the effective operating range of the pump is between the fluid level and the top of the liner. The actual liner to be cleaned is typically three times longer than this effective range of the pump. In order to clean sand from the entire liner section, the pump must be removed from the well periodically to add more tubing below it to reach farther into the liner. This is a time consuming and hence expensive operation. In most cases, stroke type pumps are only successful in cleaning out the first 1/3 to 1/2 of the liner section. PA1 (2) CIRCULATING DEVICES--Due to the low fluid level typically encountered in wells to be cleaned out, conventional circulation techniques are not possible. Circulating devices currently in use involve the use of multiple tubing strings (either parallel or concentric) to convey fluid from surface to the sandface and from the sandface back to surface. Moving multiple strings of tubing axially within the wellbore is complicated and expensive. In addition, use of an expensive gel type fluid is typically necessary in such devices in order to carry the relatively heavy sand to surface. PA1 (3) COMBINATION DEVICES--Certain devices that utilize a combination of multiple tubular strings and downhole pumps have been employed with varying degrees of success. These devices are typically slow and expensive to operate for the same reasons as shown above.
Sand clean-out methods incorporating such devices are ineffective and inefficient due to cost, time or capacity limitations.
Downhole rotational pumps are devices which are conventionally used in pumping fluid in oil or gas formations, from a static location in a wellbore.
It is an object of the present invention to provide an apparatus and method which will effectively and economically clean sand and such debris out of such wells.